Two lamp light comparison type densitometer

ABSTRACT

Two lamps are lighted alternately at controlled intensities, both lamps illuminate a common sensor and the light path from one lamp includes the density to be measured. When a minimum differential is detected, the ratio of the currents in the lamps is a function of the density being measured and current in either one or both lamp is servo-controlled to minimize the differential. The current or voltage ratios are converted and read out as density values.

United States Patent Barge [451 Apr. 4, 1972 [54] TWO LAMP LIGHT COMPARISON TYPE DENSHTOMETER [72] Inventor: Ralph L. Berge, Binghamton, NY.

[73] Assignee: GAF Corporation, New York, N.Y.

[22] Filed: Aug. 19, 1969 I [21] Appl. No.: 851,320

[52] US. Cl. ..356/205, 250/219 FR, 250/228, 356/212 [51] Int. Cl ..G01n21/22,G01n21/48 [58] Field of Search ..356/201, 204, 205, 202, 195, 356/212; 250/228, 219 FR [56] References Cited UNITED STATES PATENTS 2,594,514 4/1952 Sweet ..356/205 3,079,835 3/1963 Saperstein ..356/l52 3,413,482 11/1968 Ling ..250/43.5X

Primary Examiner-Ronald L. Wibert Assistant Examiner-Orville B. Chew, ll

Attorney-Walter G. l-lensel, George L. Tone and Martin Smolowitz '57 ABSTRACT 2 Claims, 4 Drawing Figures VOLTAGE r0 DENSITY CONVERSION READ our .50 52 PHASE SENSITIVE 3g DETECTOR a AMPL/FIER l CURRENT REGULATOR OSCILLATOR & ELECTRON/C g SWITCH W 7 e PATENTEUAPR 4:972 3,653,772

sum 1 OF 2 VOLTAGE T0 DENSITY CONVERSION &

READ our 45 ,1 -50 52 PHASE SENS/T/VE DETECTOR a 7X AMPLIFIER 4 CURRENT REGULATOR OS/LLATOR & ELECTRON/C 51 SWITCH W 7 '52 3 M 1B 5% 4 @512. faga/i'l'f'fj PATENTEHAFR 4 I972 SHEET 2 OF 2 F PHASE SENSITIVE DETECTOR ELECTRONIC SWITCH CURRENT REGULATOR AMPL IF IE R L AMP VOL T AGE DENSITY CONVERSION NETWORK 447, DENSITY w READ our 2 INYjNTZR B I xonm-zv j TWO LAMP LIGHT COMPARISON TYPE DENSITOMETER This invention relates to light comparison meters and particularly to two lamp densitometers.

It has been proposed to use two series-connected lamps in a light brightness meter to illuminate a sample and a photocell, respectively, and then adjust the current flowing through such lamps from a common source of supply until the sample visually matches a comparison spot in color. whereupon the output of the photocell provides a measure of the brightness of such sample. Such proposal is disclosed by US. Pat. No. 2,933,010, to Petro Vlahos, dated Apr. 19, 1960.

Comparison photometers employing visual indicating means to an observer are also disclosed by US. patents to Cooper, Jr., US. Pat. No. 3,323,430 (1967), and Biber et al., U.S. Pat. No. 3,413,066 (1968), for example.

Comparison densitometers are also known that mechanically chop light from a common source such as a lamp, for illuminatin g a sensor to compare a sample with a standard.

In any case movable mechanical parts used in prior comparison densitometers have limited the availability due to cost thereof where accuracy was a factor. The present invention solves such problem by providing a low-cost, accurate, comparison densitometer having no moving mechanical parts.

SUMMARY According to the invention, a primary lamp and a reference lamp are alternately electrically energized. Both lamps are arranged to illuminate the same sensor. The reference lamp is servo-powered to minimize the A.C. error difference sensed by the sensor, a CDS Cell. The level of the reference drive voltage is, therefore, a function of the reflection, or transmission path, of the primary light. Since the turn-off and turn-on time of small lamps is of the order of 0.01 seconds, the sampling frequency can be any rate below 50-a Novel optical systems are provided to shade the lamps from each other, while at the same time, the light rays therefrom are directed and/or focused on the eye of the same sensor. The primary light may either pass through a sample, or be reflected by a sample depending upon the nature or type of density being measured. In either case, no moving parts, such as light chopping means are needed; and an accurate reading is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are optical and circuit diagrams, respectively, of apparatus illustrative of the invention;

FIG. 3 is a diagram of a modified optical system in which the primary light passes through the sample;

FIG. 4 is a diagram of another modification.

PREFERRED EMBODIMENT As shown in FIG. 1, a primary lamp and a reference lamp 12 are located in the opposing recesses 14 and 16 of a light impervious shade 18, so that light from the reference lamp shines directly on a sensor 20. Light from the primary lamp 10 is directed toward a spot 22 on sample 24, through a double convex lens 26. Light reflected from the sample spot 22 is directed toward the sensor by a plurality of spheric mirrors 28,28 that are spaced from opposite sides of the shade 18.

The lamps 10 and 12, FIG. 2, are alternately energized from a common source of supply, such as a battery 28, by the operation of an electronic switch 30, typically composed of a multivibrator and two transistor switches.

For example, when the switch reed or blade 31 touches contact 34, circuit 36 conducts current from the battery or stable supply 28 to lamp 10. The return flow of such current is through ground connection 38. Such current energizes and lights lamp 10. However, when switch blade 32 leaves contact 34, such current flow to lamp 10 ceases and current flow is established in circuit 40, which leads to lamp 12 through a voltage regulator 42. Thus, as the switch blade swings from one contact to the other, the lamps 10 and 12 are alternately energized, so that the corresponding light from each is alternately applied to the same sensor 20.

The sensor 20 is connected between ground 38 and a circuit 4 containing a phase sensitive detector 46 and the current regulator 42. Such circuit functions as a servo-power source to minimize the A.C. error difference sensed by the sensor 20, such as a CD8 cell. As a result, the level of the reference drive voltage at terminal 48 is a function of the density of the reflection of the primary light which originates in lamp 10. Such voltage is applied via lead 50 to a desnity conversion and read out circuit 52 that is connection also to ground 38. The read out" indicates the density of the spot 22 of sample 24.

TRANSMISSION DENSITOMETER I As shown in FIG. 3, sensor is located within an internally mirrored sphere 52 having an opening 54 through which light shines on the eye of the sensor 20 from a double convex lens 56. The lens 56 collects light from the primary lamp 10, which 1 APPARATUS MODIFICATION As shown in FIG. 4, a light shield 62 is disposed between the lamps l0 and 12, so that light from lamp 12 shines directly in v the eye of sensor 20, while that from lamp 10 is reflected from sample 24 above the shield 62 into such eye. Output from the sensor 20 goes to the phase sensitive detector, and from the latter to amplifier 64. The lamp 12 is energized by battery 28 through the electronic switch 30 and voltage regulator 42; while the lamp 10 is also energized through such switch 36.

Thus, reference lamp 12 is automatically energized so that its light output equals that of the primary lamp 10 as reflected by the sample 24, by a corresponding change in the voltage applied to.such lamp 12. Such voltage is transmitted to to a lamp-voltage-to-density-conversion network 64 which operates a density read out device 66. The latter thus, indicates the density of the sample 24, as the electronic switch alternately connects the lamps l0 and 12 to the battery 28.

In some applications an arrangement where the sensor light level is constant will be useful. The current and intensity of the reference lamp is held at a low level by resistor R. The intensity of the primary lamp or lamps is controlled to compliment the density of the sample. The primary lamp would shine through the sample for transmission measurement, or be clustered about the sensor shell for reflection measurement, as shown.

For the purpose of reading color densities, complimentary filters are interposed into the primary light path. At the same time the voltage to density conversion network is switched to provide a matching conversion for each color.

ADVANTAGES OF THE INVENTION The invention makes possible an accurate densitometer in which no moving parts are present, inasmuch as solid elements can be used throughout the system.

Another major advantage is that the system can be made at low cost.

Light weight and compactness constitute additional advantages, especially where portability and space savings are factors.

What is claimed is:

1. A comparison densitometer comprising, in combination:

a sensing means for comparing light of a sample with that of a standard;

means including one electric lamp for illuminating said sensor with reference light;

an internally mirrored sphere having disposed therein, said sensor and one of said lamps, said sphere having an opening for light originating in the other lamp.

2. The invention as defined by claim 1, in which the lamp within the sphere produces the reference light, and

the lamp outside of the sphere produces the sample light which passes through such selected portion of the sample and then through such opening in the sphere on its way toward said senses.

Disclaimer 3,653,772.Ralph I. Berge, Binghamton, N.Y. TWO LAMP LIGHT COMPAR- ISON TYPE DENSITOMETER. Patent dated Apr. 4,1972. Disclaimer filed Sept. 30, 1982, by the assignee, Eastman Kodak Co.

Hereby enters this disclaimer to all claims of said patent.

[Oflicial Gazette April 5, 1983.] 

1. A comparison densitometer comprising, in combination: a sensing means for comparing light of a sample with that of a standard; means including one electric lamp for illuminating said sensor with reference light; means including another electric lamp; optical means for illuminating said sensor with sample light for comparison with such reference light, said optical means including light impervious shade means disposed between said lamps; lens means for concentrating the sample light on a circuited portion of the sample, circuit means for electrically energizing said lamps alternately from a common source of supply at a rate sufficiently low to turn the light of said lamps on and off; and an internally mirrored sphere having disposed therein, said sensor and one of said lamps, said sphere having an opening for light originating in the other lamp.
 2. The invention as defined by claim 1, in which the lamp within the sphere produces the reference light, and the lamp outside of the sphere produces the sample light which passes through such selected portion of the sample and then through such opening in the sphere on its way toward said senses. 